Fundus camera

ABSTRACT

A fundus camera that obtains focus evaluation values by scanning, in which a focusing lens moves a predetermined distance according to a photographing mode before the focusing lens starts scanning for obtaining focus evaluation values.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fundus camera having an automaticfocusing function.

2. Description of the Related Art

Japanese Patent Application No. 08-150121 discusses a fundus camera inwhich either a visible light mode or a near-infrared light mode isselected for observation of fundus, and an automatic focusing isperformed based on a fundus image for photographing the fundus imageusing visible light.

Conventionally, in auto-focusing by a sharpness detection system, focusevaluation values are obtained based on high frequency components withina predetermined area of a fundus image while moving a focusing lens. Thecurve profile (mountain shape) of changing values needs to be obtainedto perform auto-focusing.

To obtain the profile and a peak of a curve, a focusing lens iscontrolled as follows: first, a focusing lens moves between a − endpointand a + endpoint (in either direction) within a moving range forscanning to obtain focus evaluation values, so that a peak of theprofile of the scanned focus evaluation values is detected. After thedetection, when the following focus evaluation value drops below apredetermined value, the scanning is stopped. Then, the focusing lensreturns to the position where the peak value of the focus evaluationvalues can be acquired, and photographing is performed thereat.

FIG. 8 illustrates the above control. The horizontal axis representsmoving range of a focusing lens between a + end point for the limit ofa + diopter and a − end point for the limit of a − diopter. The verticalaxis (on the + side) represents focus evaluation value, each of whichis, for example, a sum of values for high frequency components within apredetermined area of a fundus image.

With respect to an image, the contrast is higher and thus the focusevaluation values are higher at the positions closer to the in-focusposition of an image. The curves in FIG. 8 consists of focus evaluationvalues for a case where a focusing lens is moved throughout the movingrange for scanning. Actually, however, apart of the range is scanned,resulting in a curve only for the range.

The vertical axis (on the − side) represents time with respect tomovement of a focusing lens and a sequence of scanned focus evaluationvalues. The solid line Mx represents a simple movement of a focusinglens, and the broken line Sx represents scanning for acquiring focusevaluation values, wherein x is the order of movement.

In FIG. 8, each control of a focusing lens starts at the position markedby a double circle, and ends at the position marked by a circle. Theposition marked by the triangle on the horizontal axis represents theposition of a focusing lens in the previous focusing sequence. In thecase of FIG. 8, the focusing lens was moved as illustrated in M1, S1,and M2 in this order for photographing.

So far, however, no fundus camera has come into use in which thecontrols of automatic focusing in a visible-light observation mode and anear-infrared light observation mode are optimized to reduce the timerequired for automatic focusing.

SUMMARY OF THE INVENTION

The present invention is directed to a fundus camera capable of reducingthe time required for automatic focusing by performing appropriatecontrol of an automatic focusing according to a photographing mode.

According to an aspect of the present invention, A fundus cameraincludes an observation photographing optical system having a focusinglens for focusing an image of a fundus of a subject's eye onto an imagecapturing unit, a photographing mode selection unit configured to selecta photographing mode, and a control unit configured to control aposition of the focusing lens based on focus evaluation valuescalculated using the fundus image on the image capturing unit, whereinthe control unit switches moving operations of the focusing lensaccording to the photographing mode.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 illustrates a configuration of a fundus camera.

FIGS. 2A and 2B illustrate operations of a focusing lens.

FIGS. 3A and 3B illustrate operations of a focusing lens.

FIGS. 4A and 4B illustrate operations of a focusing lens.

FIGS. 5A and 5B illustrates a scanning for obtaining focus evaluationvalues.

FIG. 6 illustrates a range for calculating focus evaluation values.

FIG. 7 is a flowchart illustrating operations according to an exemplaryembodiment of the present invention.

FIG. 8 illustrates operations of a conventional focusing lens.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 1 illustrates a configuration of a fundus camera according to thepresent exemplary embodiment. The fundus camera is provided with anobservation photographing optical system which is positioned opposite toa subject's eye E. The observation photographing optical systemincludes, in sequence, an objective lens 1, an aperture mirror 2 locatedapproximately conjugate to the pupil Ep of the subject's eye E, adiaphragm 3, a focusing lens 4, and a potentiometer 5 for detecting aposition of the focusing lens 4. The observation photographing opticalsystem further includes an imaging lens 6, a dichroic flip-up mirror 7for transmitting near-infrared light but reflecting visible light, fixedmirrors 12 and 14, and relay lenses 13 and 15. Following the relaylenses, an infrared cut filter 16 is inserted in the optical path duringphotographing, and a digital camera 41 is disposed at the end of theoptical path for observation and photographing of a fundus image.

Along the optical axis of light reflected by the flip-up mirror 7, aviewfinder optical system including a movable mirror 8, a field stop 10,and an eye-piece lens 11, and an internal fixation lamp 9 are arranged.

The digital camera 41 is mounted to the body of the fundus camera usinga removable mount. The digital camera 41 has a quick-return mirror 42, aCMOS area sensor 43, an LCD monitor 44, a processing circuit 45.

The CMOS area sensor 43 is provided with an RGB filter that passesnear-infrared radiation, and is sensitive to visible and infrared lightto capture moving and static images. To capture moving images, anamplifier in the CMOS area sensor 43 is set to high gain to generatethinned images suitable for a resolution of the LCD monitor 44 by aprocessing circuit 45, and the resultant moving images are displayed onthe LCD monitor 44.

For photographing a fundus, light is emitted from a xenon tube 23 tocapture a still image of the fundus. In this case, the amplifier in theCMOS area sensor 43 is set back to normal for obtaining a higher S/N.The resulting image data having the resolution of the CMOS area sensor43 for every pixel is developed by the processing circuit 45, and storedin a storage medium (not illustrated) in a specified file format.

FIG. 6 illustrates an area for calculating contrast of a fundus image. Afundus image 301 is formed on the CMOS area sensor 43, and contains amacula 302 and an optic disk 303. Contrast of the image is calculatedfor the area 304. The processing circuit 45 calculates a focusevaluation value, which represents a focusing level of the moving imageto be photographed, by adding signals within a range of a bandwidth thatis further limited from the high frequency components of the area 304 inthe moving image.

The focusing lens moves within a moving range to obtain focus evaluationvalues, and the focus evaluation value at each point within the range iscomplemented using, for example, a spline curve to produce a curve, sothat the peak of the curve is calculated as an in-focus position. Thecontrol unit 46 of the fundus camera controls the focusing lens to movebased on the resultant calculation. The quick-return mirror 42 in thedigital camera 41 is held in a flipped state during photographing.

If no input operation is detected for a predetermined time, the controlunit 46 controls the focusing lens 4 to move to the approximatelycentral position (0 diopter) within the moving range. The control unit46 controls the photographing to be performed at a in-focus positionmoved from a predetermined direction and stopped to reduce the influenceof backlash of the driving mechanism of the focusing lens 4, and tomaintain focusing accuracy.

In the present exemplary embodiment, the focusing lens 4 simply movesfrom the + end point to the − end point, and scans for acquiring focusevaluation values from the − end point to the + end point. Thedirections, however, may be reversed. During the scanning for acquiringfocus evaluation values, the focusing lens 4 may be moving at a lowspeed, or may stop intermittently to obtain each focus evaluation value.

In the former case, the speed needs to be slow enough so that thedistance in which the focusing lens 4 moves while obtaining a focusevaluation value does not impair focusing accuracy. In the latter case,a higher speed may be used, but this involves abrupt acceleration andsudden stop, which resulting in vibration. Accordingly, in either case,the focusing lens 4 can move for scanning to obtain focus evaluationvalues at a slower speed than that for simple moving.

On the illumination optical path along incident light to the aperturemirror 2, the following components are arranged in sequence toward theaperture mirror 2: a halogen lamp 27 that is a light source forobservation of fundus; a diffusion plate 26; a condenser lens 25; avisible-light cut filter 24; a xenon tube 23 that is locatedapproximately conjugate to a pupil Ep of a subject's eye E; a ring slit22; a condenser lens 21; a fixed mirror 20; relay lenses 18 and 19; anda cornea baffle 17.

For fundus observation, a light beam is emitted from the halogen lamp 27and passes through the visible-light cut filter 24, so that a fundus isilluminated with the transmitted near-infrared light. For photographing,the halogen lamp 27 is turned off, and light is emitted from the xenontube 23 to illuminate the fundus.

The control circuit 46 controls insertions and retractions of theflip-up mirror 7, the movable mirror 8, the filters 16 and 24, andpositioning of the focusing lens 4, and communication with the digitalcamera 41. The control circuit 46 is also connected to a photographingswitch 50, a right/left eye detection switch 49 for detecting adirection of an eye to be photographed, a photographing mode switch 48,and a storage circuit 47 that stores a position of the focusing lens indatabase for each mode or each photographing with date and on aweek-to-week basis.

The positional data in the database can be used, for example, as adistribution of photographing for a month in a photographing mode, sothat the focusing lens 4 is moved to a position according to the data.The optical system of the fundus camera is mounted in a housing. Whenthe housing is moved to be adjusted to a subject's right/left eye, theright/left eye detection switch 49 is turned on/off to detect thedirection of the eye to be photographed.

In the fundus camera having the above described configuration, thephotographing mode switch 48, which is a photographing mode selectionunit, is used to select one of a mydriatic photographing mode and anon-mydriatic photographing mode. When the mydriatic photographing modeis selected, the visible-light cut filter 24 retracts from the opticalpath, and the infrared cut filter 16 is inserted in the optical path.

For automatic focusing, the flip-up mirror 7 retracts from the opticalpath. A light beam is emitted from the halogen lamp 27 to pass throughthe infrared cut filter 16. The transmitted visible light beam passesthrough the ring slit 22 and the condenser lens 21, is reflected by thefixed mirror 20 and the aperture mirror 2 around the aperture to passthrough the objective lens 1 to the pupil Ep of the subject's eye E.Then, the visible light beam is incident on the fundus Er to illuminatethe fundus with the visible light.

The light beam is reflected by the fundus Er to pass through the centerof the pupil Ep, the objective lens 1, the aperture of the aperturemirror 2, the diaphragm 3, and the focusing lens 4 to be reflected bythe fixed mirrors 12 and 14, and pass through the infrared cut filter16. The light beam is focused onto the CMOS area sensor 43 in thedigital camera 41 for capturing an image.

When the non-mydriatic photographing mode is selected using thephotographing mode switch 48, which is a selection unit, thevisible-light cut filter 24 is inserted into the optical path, and theflip-up mirror 7 moves into the optical path. The movable mirror 8shifts to the position illustrated by the broken line, and the infraredcut filter 16 retracts from the optical path.

A light beam is emitted from the halogen lamp 27 to pass the infraredcut filter 16, where a near infrared range of the beam is extracted. Theextracted near-infrared light beam is similarly reflected by theaperture mirror 2 around the aperture to pass through the objective lens1 to illuminate the fundus Er of the subject's eye E. The near-infraredlight beam is reflected by the fundus Er to pass through the objectivelens 1, the center of the aperture mirror 2, the focusing lens 4, andthe flip-up mirror 7, which is a dichroic mirror.

The light beam is then reflected by the fixed mirrors 12 and 14 to befocused on the CMOS area sensor 43 for capturing an image. A fundusimage captured in the CMOS area sensor 43 is displayed on the LCD 44 asa moving image. An operator can perform alignment using a control stick(not illustrated).

In the non-mydriatic mode, with the movable mirror 8 being retractedfrom the optical path, a visible light beam from the internal fixationlamp 9 is reflected by the flip-up mirror 7, and passes through thefocusing lens 4, the center of the aperture mirror 2, and the objectivelens 1 to be projected onto the fundus. Thus, a subject's eye can stareat the turned-on light source image of the internal fixation lamp 9. Thedirection of the fundus is controlled by adjusting the light emittingposition of the internal fixation lamp 9 using a switch (notillustrated). In the mydriatic mode, the other eye, which is not asubject's eye, is controlled to stare at an external fixation lamp (notillustrated), and the position of the fundus is adjusted.

When a finder is used in the mydriatic mode, the flip-up mirror 7 andthe movable mirror 8 are inserted into the optical path by operating aswitch (not illustrated). A visible light beam reflected by a fundus isreflected and guided by the flip-up mirror 7 and the movable mirror 8into the viewfinder optical system. The light beam from the fundus doesnot enter the digital camera 41, and thereby no automatic focusingcontrol is performed. Focus adjustment of the optical system isperformed by rotating a knob (not illustrated) to move the focusing lens4.

When the fundus is aligned with the optical system and the photographingswitch 50 is half pressed, the control unit 46 causes the focusing lens4 to move in the direction of − diopter values (− direction) by apredetermined distance and then to move for scanning in the directionof + diopter values (+ direction) to obtain focus evaluation values. Thepredetermined distance is determined according to a photographing mode.

Focusing control will be described below with reference to FIG. 2. Whenfocusing is completed, the completion is notified to the operator by adisplay (not illustrated) or sound, so that the operator fully pressesthe photographing switch 50 to flip up the flip-up mirror 7. Thisoperation is required in the cases where a finder is used in thenon-mydriatic mode or the mydriatic mode. As a result, the infrared cutfilter 16 is inserted into the optical path (in the non-mydriatic mode)for photographing using light from the xenon tube 23.

The peak position of the focus evaluation values in the non-mydriaticmode is corrected by moving the focusing lens 4 before light is emittedfor photographing, because the focusing position is different from thatin mydriatic mode, which uses visible light for fundus illumination, andslightly behind the retina Er.

FIGS. 2A to 4B illustrate controls of a focusing lens for automaticfocusing. Controls in the mydriatic mode using visible light forillumination are illustrated in FIGS. 2A, 3A and 4A, and controls in thenon-mydriatic mode using near-infrared light for illumination areillustrated in FIGS. 2B, 3B and 4B. Throughout the figures, the samesymbols have the same meaning respectively.

The horizontal axis represents a moving range of the focusing lens 4,with the + end point to the right hand side and the − end point to theleft hand side. The vertical axis on the + side represents focusevaluation value, whereas the vertical axis on the − side representstime when the focusing lens 4 is driven. The inverted triangle markrepresents a previous position of the focusing lens 4, the double circlemark represents a position where a current sequence for driving thefocusing lens 4 starts, and the ∘ (circle) mark represents a positionwhere focusing is completed.

Each of the solid lines represents a simple movement of the focusinglens 4, whereas each of the broken lines represents a movement withscanning for obtaining focus evaluation values of the focusing lens 4.The mark L1 illustrates a threshold as a level of a focus evaluationvalue for determining positions where the focusing lens 4 is stopped orreturned.

FIGS. 2A and 2B each illustrate an evaluation value curve (i.e., a curvefor focus evaluation values) over the entire range scanned by thefocusing lens 4. Actually, however, the range between the verticalbroken lines is scanned for sampling focus evaluation values, and thecurve only for the range is obtained. The mark W means a movement of apredetermined distance by the focusing lens 4.

FIGS. 2A and 2B each illustrate a control of a focusing lens accordingto the photographing modes, in the case where an eye to be photographedhas a less refractive power as compared to that in a previousphotographing.

In FIG. 2A (in the mydriatic mode) when the photographing switch 50 ishalf pressed, the focusing lens moves the distance W (M1) in the −direction from the position with the double circle, and the focusevaluation value at the position is set to a threshold (L1). Then, thefocusing lens returns in the + direction to start scanning for focusevaluation values (S1). When the obtained focus evaluation value becomeequal to or less than the threshold, and a peak value is detected, thefocusing lens stops the scanning, and moves back in the − direction tothe peak position (M2), and stops there (at the circle-mark position).

At this point of time, the focusing control is completed, which isnotified to the operator by a display (not illustrated) or sound. Theoperator watches and observes the LCD monitor 44 to determine whether ornot the target fundus site is displayed on the monitor. If so, theoperator fully presses the photographing switch 50 to cause the xenontube 23 to emit light for photographing a still image of the fundus.

Photographing in the non-mydriatic mode will be described with referenceto FIG. 2B. In the description, the position where the focusing lens 4starts to move, and the fundus to be photographed are the same as thosein the above-described mydriatic mode.

First, the focusing lens moves the distance W in the − direction. Thedistance W is longer than that in the mydriatic mode. In thenon-mydriatic mode using near-infrared light for fundus illumination, afundus image to be photographed has a lower contrast, and thereby focusevaluation values to be obtained are smaller than those in the mydriaticmode using visible light.

The obtained focus evaluation values produce a curve that has a profilewith a lower peak and longer trails. Accordingly, an accurate detectionof an in-focus position requires scanning within a larger width. Thefocusing lens 4 moves the distance W (M1) in the − direction and stopsthere. The focus evaluation value at the stopped position is set to athreshold (L1). Then, the focusing lens 4 returns to the + side to startscanning for obtaining focus evaluation values (S1). The remainingoperations for focusing are the same as those in the mydriatic mode.

The difference in scanning for obtaining focus evaluation values betweenin the mydriatic mode and in the non-mydriatic mode will be describedwith reference to FIGS. 5A and 5B. FIG. 5A illustrates a curve in themydriatic mode. The horizontal axis represents the amount of movementsof the focusing lens 4, whereas the vertical axis represents the focusevaluation value. The focus evaluation values S1 to S10 are obtained forevery pitch p1 as the focusing lens 4 moves.

In the mydriatic mode using visible light for fundus illumination, afundus image to be photographed has a higher contrast, and the obtainedfocus evaluation values produce a curve that has a sharp profile.Accordingly, an accurate detection of an in-focus position requiresscanning within a small width (i.e., the distance the focusing lensmoves) at a low speed.

In FIG. 5B for the non-mydriatic mode, the focus evaluation values S1 toS11 are obtained for every pitch p2 as the focusing lens 4 moves. Sincethe fundus is illuminated with near-infrared light, a resulting fundusimage has a lower contrast. As a result, the obtained focus evaluationvalues produce a curve of a gently sloping profile.

Accordingly, focus evaluation values may be obtained at wider pitchesthan those in the mydriatic mode, which increases the distance forscanning. Fortunately, the scanning can be achieved at a higher speedthan that in the mydriatic mode, and the total periods of time forscanning for focusing are equal to each other in these modes.

FIG. 3 illustrates a case where an eye to be photographed has a greaterrefractive power as compared to that in a previous photographing. Thecontrol of a focusing lens in the mydriatic mode illustrated in FIG. 3Ais similarly performed as in the case of FIG. 2, except the following.

After the focusing lens 4 moves the distance W (M1) and obtains focusevaluation values, the focus evaluation value at the position is set toa threshold L1. Then, the focusing lens 4 starts scanning for focusingin the + direction (S1). When a highest focus evaluation value isdetected, the difference (h) between the highest value and the thresholdL1 is compared with a reference value. If the comparison indicates thatthe highest value is sufficiently large, the focusing lens 4 stops thescanning when a scanned value becomes smaller than the peak value byh/2, and the focusing lens 4 moves back to the position with the highestvalue (M2).

The operations in FIG. 3B for the non-mydriatic mode are the same asthose in FIG. 3A, but the value h that is the difference between ahighest value and the threshold L1 is compared to a reference value forthe non-mydriatic mode, instead of the reference value for the mydriaticmode. The focus evaluation values in the non-mydriatic mode produces acurve of a gently sloping profile with an unclear peak, resulting in alower reference value. The other control operations are the same asthose in the mydriatic mode.

FIG. 4 illustrates a case where a focusing position is offset from thatin a previous photographing by more than a predetermined distance W. Inthe mydriatic mode, the focusing lens 4 moves the distance W (M1) in the− direction. After focus evaluation value is obtained and a newthreshold is set, scanning in the + direction (S1) is started.

The scanning is then stopped because the focus evaluation valuescontinuously drop, and the focusing lens 4 moves the distance of 2 Wfrom the start position in the − direction (M2). After focus evaluationvalue is obtained and a new threshold is set, scanning in the +direction (S2) is started. The scanning, however, is again stoppedbecause the focus evaluation values continuously drop.

Then, the focusing lens 4 moves the distance of 3 W from the startposition in the − direction (M3). After focus evaluation value isobtained and a new threshold is set, scanning in the + direction (S3) isstarted. When a highest focus evaluation value is detected and thefollowing focus evaluation values go below the threshold, the scanningis stopped. The focusing lens 4 moves in the − direction to the peakposition (M4), and the focusing control ends.

In this case, since the difference between the highest value and thethreshold is below a reference value, the scanning (S3) is performeduntil focus evaluation value goes below the threshold. In thenon-mydriatic mode, a distance W for non-mydriatic mode is used. In thenon-mydriatic mode, focus evaluation values produce a gently slopingcurve, and thereby an in-focus position can be determined after themovement of the distance W is repeated twice.

FIG. 7 is a flowchart illustrating the focusing operations in from FIGS.2A and 2B to FIGS. 4A and 4B. The focusing routine is performed from“START” to “END”.

In step S101, a photographing mode is determined. If it is determined tobe a mydriatic mode (mydriatic mode in step S101), then in step S102, adistance W1, a scan speed v1, and a reference value S1 are set. If it isdetermined to be a non-mydriatic mode (non-mydriatic mode in step S101),then in step S103, a distance W2, a scan speed v2, and a reference valueS2 are set.

In step S104, a peak flag for storing a presence/absence of a previouspeak is cleared, and the number of movement of the focusing lens N isset to 1, and the peak height h of a previous curve of focus evaluationvalues is cleared. In step S105, the focusing lens moves in the −direction from a starting point to a point at the distance N×W.

If the target point is beyond the − end point, the focusing lens isstopped at the − end point. In step S106, the focus evaluation value atthe current position is obtained to set a new threshold. In step S107,the focusing lens starts to move in the + direction for obtaining focusevaluation values at predetermined intervals. In step S108, a focusevaluation value is obtained.

In step S109, it is determined whether or not a peak is detected. Thedetermination is made by checking whether or not the focus evaluationvalue increase to the peak by a predetermined value and decrease fromthe peak by the predetermined value within a certain distance of themovement of the focusing lens. If a peak is detected (YES in step S109),then in step S110, a peak flag is set on, and a value h is set as adifference between the peak value of the focus evaluation value and thethreshold.

In step S111, the value h is compared with the reference value, and ifthe value h is greater than the reference value (YES in step S111), thenin step S112, a new threshold is set to a value smaller than the peakvalue by the value h/2. In step S113, the focus evaluation value iscompared with the threshold, and if the focus evaluation value issmaller than the threshold (NO in step S113), the process proceeds tostep S114, and otherwise (YES in step S113), the process proceeds tostep S115.

In step S114, it is determined whether or not the focusing lens 4 hasreached the + end point, and if the focusing lens 4 has not reachedthe + end point yet (NO in step S114), the process returns to step S108for detecting a next peak. If the focusing lens 4 has reached the + endpoint (YES in step S114), then in step S117, the scanning is stopped.

In step S120, since no peak has been detected, the focusing lens 4returns to the initial point. The initial point is approximately thecenter of the moving range of the focusing lens 4, and corresponds to 0diopter.

In step S115, it is determined whether or not a peak flag is set on. Ifa peak is already detected (YES in step S115), in step S118, thescanning is stopped. In step S121, the focus evaluation value at eachpoint is complemented using, for example, a spline curve to produce acurve, so that a peak of the curve is calculated, and the focusing lens4 moves to the peak position. Then the focusing routine ends (END).

If no peak flag is set on in step S115 (NO in step S115), in step S116,it is determined whether or not focus evaluation values are obtained apredetermined number of times in a row. In other words, it is determinedwhether or not the obtained focus evaluation values are below thethreshold continuously.

If focus evaluation values are obtained in sequence (YES in step S116),then in step S119, the number N is incremented by 1 (N=N+1) and thescanning is stopped. Then, the process returns to step S105 to repeatthe process therefrom. If focus evaluation values are not obtained insequence (NO in step S116), the process returns to step S108 to repeatthe process therefrom.

In the flowchart, the focusing lens moves in the − direction, and thescanning is performed in the + direction for obtaining focus evaluationvalues. The directions, however, may be reversed. The values W1 and W2and the values v1 and v2 are specified under the condition: W1<W2 andv1<v2 as described above with reference to FIG. 5. Accordingly, thepredetermined distance of movement in the mydriatic mode is less thanthat in the non-mydriatic mode, and the scanning speed in the mydriaticmode is slower than that in the non-mydriatic mode.

There exists a method of photographing in mydriatic mode that usesvisible fluorescent or a red-free light within much narrower visiblewavelengths than those in color photographing. In this case, an image ofa higher contrast can be obtained than that in the above describedmydriatic mode, and thereby the predetermined distance of a firstmovement of a focusing lens can be further reduced.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2009-162848 filed Jul. 9, 2009, which is hereby incorporated byreference herein in its entirety.

1. A fundus camera comprising: an observation photographing opticalsystem having a focusing lens for focusing an image of a fundus of asubject's eye onto an image capturing unit; a photographing modeselection unit configured to select a photographing mode; and a controlunit configured to control a position of the focusing lens based onfocus evaluation values calculated using the fundus image on the imagecapturing unit; wherein the control unit switches moving operations ofthe focusing lens according to the photographing mode.
 2. The funduscamera according to claim 1, wherein the control unit changes apredetermined distance in which the focusing lens moves, according tothe photographing mode.
 3. The fundus camera according to claim 2wherein, when the non-mydriatic photographing mode is selected by thephotographing mode selection unit, the control unit increases thepredetermined distance as compared to that when the mydriaticphotographing mode is selected by the photographing mode selection unit.4. The fundus camera according to claim 1, wherein the control unitchanges a moving speed of the focusing lens according to thephotographing mode.
 5. The fundus camera according to claim 4 wherein,when the non-mydriatic photographing mode is selected by thephotographing mode selection unit, the control unit increases the movingspeed of the focusing lens as compared to that when the mydriaticphotographing mode is selected by the photographing mode selection unit.6. The fundus camera according to claim 1, wherein the control unitchanges a pitch of movement of the focusing lens for obtaining the focusevaluation values, according to the photographing mode.
 7. The funduscamera according to claim 6 wherein, when the non-mydriaticphotographing mode is selected by the photographing mode selection unit,the control unit increases the pitch of the focusing lens for focusingas compared to that when the mydriatic photographing mode is selected bythe photographing mode selection unit.
 8. The fundus camera according toclaim 1, wherein the photographing mode selection unit selects one of amydriatic photographing mode where the fundus of the subject's eye isilluminated with visible light, and a non-mydriatic photographing modewhere the fundus of the subject's eye is illuminated with near-infraredlight.